The present invention concerns a novel apparatus and method for inducing and detecting fluorescence. The apparatus is particularly useful for measuring fluorescence emitted from turbid or highly turbid fluid media, such as, e,g., fluorescence emitted from living cells in a fermentation tank or in a mixed culture in a water purification plant. Thus, the apparatus is most valuable for performing the fluorescence determinations in the method disclosed in WO90/10083 published 7 Sep. 1990, which relates to a method for controlling and/or optimising a process in which an aqueous system comprising biodegradable material, such as waste water or sewage, is subjected to biological treatment using mixed cultures of microorganisms.
U.S. Pat. No. 4,577,110 discloses an apparatus for inducing fluorescence in, and measuring fluorescence emitted from, a biological medium. The apparatus is adapted to launch, from a continuous light source, a beam of exciting light through a ring-shaped detector. The apparatus is designed so that the field of illumination of the exciting light is substantially contained within the field of view of the detector measuring the emitted fluorescence.
EP 0.047.094 discloses an apparatus for inducing and detecting fluorescence in a medium. The pulsed exciting light and the fluorescence emitted from the medium are guided to and from the measured medium by means of optical fibres.
In highly turbid media, light is not able to travel more than a few mm or even only fractions of a mm before it becomes very considerably attenuated. Therefore, fluorescence measurements in such media present severe problems, and there is a considerable demand for fluorescence measuring equipment which is able to perform measurements with a high sensitivity and over a broad dynamic range.
The present invention relates to an apparatus of a novel type which is particularly adapted for performing the inherently very difficult fluorescence measurements in highly turbid media, but which will also be advantageous for applications in less turbid or non-turbid media.